Place the potatoes in a saucepan with 8 cups of cold water and 1 tablespoon of coarse salt. Bring to a simmer, cover, and cook until a knife easily slips into the potatoes, about 30 minutes. Drain the potatoes and peel them.
Pass the potatoes through a potato ricer into a large bowl.
Slowly pass the potatoes through the potato ricer.
In a small saucepan, heat the milk until it comes to a boil. Meanwhile, transfer the riced potatoes to a Dutch oven or saucepan. Over medium-low heat, add the chilled butter cubes to the potatoes and stir continuously for about 5 minutes, until smooth and creamy.
Pour in the very hot milk in a thin stream, stirring briskly. Continue stirring until all the milk is absorbed. Turn off the heat and add 2 1/4 teaspoons of salt and ground white pepper.
Serve the mashed potatoes immediately. If desired, add a small cube of butter on top before serving.